For liquid containers, such as metal cans or coated cardboard receptacles for a resealable opening and easy pouring, use is often made of closure units, preferably made from plastic, and which comprise a pouring part with a pouring opening and a closure part closing the pouring opening of the pouring part and fitted in an opening of the container. Swiss patent application 2739/91-2 and 2740/91-9, PCT application No. WO 93/05945 and pending U.S. patent application Ser. No. 08/050,417, filed May 14, 1993, and based on the aforesaid PCT application all (application date 17.9.91) describe such closure units. The described closure units are molded in accordance with a multimaterial injection molding process and are made from at least two materials differing in at least one characteristic.
For easy handling in the case of the closure unit of application 2740/91, it is required that the closure unit in normal use is always connected to produce a single entity with the container in such a way that, even in the open state, the closure part cannot be completely removed from the pouring part. For fulfilling this requirement one or more flexible webs were proposed connecting the closure part in a flexible manner with the pouring part or shaped on the closure part and secured between the container and the pouring part. The disadvantage of this connection between the pouring part (or container) and the closure part is that the latter in the open state has no clearly defined position, so that a positioning movement is necessary prior to an effective closing movement to bring about a closure. As a function of the movement, the web is also deformed at different places on opening or closing. In order that the material should not be rapidly fatigued excessively as a result of these deformations and breaks, the material must either be very flexible or the web must be very thin. As the web is preferably made from the same material as the closure part and in particular its outer areas, a restriction of the material choice by the web requirements is undesired an da very thin web is not sufficiently tensionable.
Closure units molded from one material are also known which have connecting webs between the pouring part and the closure part. The closure unit is produced in the open state and closed before or after assembly on the container. The web connection has the same disadvantages as the connecting webs according to Swiss patent application 2740/91.